With the world's population topping seven billion, ABC News spoke to Fion Ngan about what it's like to live in Hong Kong, one of the world's most densely populated places.

"Hong Kong is my home. I was born and raised there, then moved to Canada with my family when I was 14. I hadn't been back to Hong Kong for more than eight years before I returned last year to visit my family for three weeks.

"I am glad I have lived in such a vibrant city like Hong Kong, a place never goes to sleep."

"Air pollution problem is a big concern for all the Hong Kong people. Hong Kong is a dense city and public transportation is one of the main causes of the air pollution. During my most recent visit, I couldn’t even see the other side of the harbour from The Peak."

"[Population hitting 7 billion] is a wake-up call for every human being in the world. Our planet is under a lot of stress due to rapid human population growth. Overpopulation causes numerous problems, and at the end human will suffer the consequences."

"Hong Kong is one of the most densely populated cities in the world. Imbalance in housing supply and demand is the biggest issue to Hong Kong people. To maximize the use of lands and the profits of the developers, the residential buildings are built as tall as they can go, and there're no space between each buildings, which local people called them 'partiperty'."

"And most of the units are tiny. A normal 4-person family home is only about 300 sq ft. In my opinion, the lesson here is when you are so limited in natural resources like the land supply in Hong Kong, you have to make it up by implementing and executing a superior urban planning program. Furthermore, the gap between rich and poor has to be minimised. Otherwise, the society remains imbalanced even if the city achieves financial success. I believe harmoniousness is the better way to measure the livability and attractiveness of a city/country."